1. Field of the Invention
The present invention relates to therapeutic radiology. More particularly, the present invention is directed to radioactive materials contained in polymers for use in therapeutic applications known as brachytherapy.
2. Background of the Invention
Treatment of cancerous tissue by exposure to radiation-emitting material is now a well established and accepted practice. Generally, the aims of such a practice include targeting exposure of radiation to the tissue surrounding or adjacent to a radiation source while keeping the radiation effects on neighboring healthy tissue to a minimum. A major advantage of this form of treatment is that it concentrates the emitted radiation at the site where the treatment is needed, e.g. within or adjacent to a tumor, while keeping the amount of radiation transmitted to the healthy tissue far below what it otherwise would be if the radiation were beamed into the body from an external source, using other forms of teletherapy.
Prior art forms of brachytherapy typically include various processes such as placing the source(s) typically small metallic capsules, approximately 4.5 mm long and 0.8 mm in diameter, called seeds containing a radiation sources such as iodine-125, cesium-131, or palladium-103, which are placed within the tissue to be treated, i.e. interstitial therapy. In various embodiments of the construction, the capsule is typically designed to allow the rapid and facile insertion of the seed into the organ or body part being treated, with minimal trauma to the targeted and surrounding tissues. These devices are many times inserted into the body percutaneously using a hollow needle which is preloaded with the desired number of therapy seeds. When the needle is in the desired location in the tissue, a stylet is used to hold the seeds in place while the needle is withdrawn from around them, leaving the seeds in the desired location. The use of such small radiation sources is a common way of practicing interstitial brachytherapy.
In many such methods it is typically considered necessary and in some cases crucial to enclose the radioactive material with an encapsulating material so as to contain the radioactive material and preventing it from becoming systemically distributed within the patient or escaping into the environment where it could contaminate medical personnel, medical facilities or the general environment. Various types of encapsulating devices and materials have been utilized and are presently contemplated. Typically these materials contain the radioactive material while allowing photon radiation (Auger x-rays) to irradiate cancerous tissues while the radioactive source decays to negligible activity. Typically, the metallic seed remains permanently implanted. A further polymer embodiment containing the radioactive source may gradually dissolve in the body after the radioactive source has decayed to negligible activity.
Another major drawback for metal-encapsulated seeds is that the encapsulating metal absorbs a significant fraction of the low-energy beta and photon radiation emitted by the contained radioisotope, for example about 14% of the iodine-125 x-rays and 40% of the palladium-103 x-rays are absorbed in the encapsulating metal in the current commercial seeds. As a consequence, to obtain the desired radiation dose rate on the exterior of the seed, an additional amount of relatively costly radioisotope activity must be added to overcome the losses in the encapsulating metal. Also, because it is typically necessary to seal (or weld). the ends of the capsules, the effective thickness of the metal is not the same in all directions resulting in a radiation field around the seed which is not uniform, a fact that complicates treatment planning and raises the possibility of the existence of areas within the treatment volume in which the radiation dose is non-uniform or below that required to kill all tumor cells present.
Thus the current practice of brachytherapy based on the use of discrete encapsulated sources is limited by: the need to associate groups of discrete seeds together by some means so that they can be placed into tissue in a predetermined array and held in that array throughout the therapeutic life of the sources, the need for complex treatment planning that takes into account the discrete nature of the seeds and the shape of the radiation field around each seed with the assumption the field shape around each seed is uniformly the same, the need to add excess radioactivity to compensate for the radiation absorption in the encapsulating metal, and the creation of a nonuniform radiation field around the source because the geometry and effective thickness of the encapsulating metal is not the same in all directions, and the radiation field about a source is not precisely spherical. The present invention as disclosed herein, significantly reduces each of these limitations and furthermore allows a more complete realization of the potential benefits of brachytherapy. The present invention includes a device, method and system for implementing brachytherapy and creating devices for use in such methods and systems. The present invention provides substantial advantages over the devices taught in the prior art.
Additional advantages and novel features of the present invention will be set forth as follows and will be readily apparent from the descriptions and demonstrations set forth herein. Accordingly, the following descriptions of the present invention should be seen as illustrative of the invention and not as limiting in any way.